The current study investigates how romantic relationships are related to antisocial behavior longitudinally among delinquent males and females (n=354; ages 14-25). While being in a relationship or not is unrelated to antisocial behavior, romantic partner characteristics (antisocial behavior and antisocial influence) are associated with greater antisocial behavior. As males age, they become increasingly resistant to romantic partner characteristics. In contrast, females become increasingly vulnerable to the effects of romantic partner characteristics on antisocial behavior as they age, particularly when these relationships are relatively shorter. Females in shorter romantic relationships with partners who are antisocial or exert antisocial influence are at risk of persisting in antisocial behavior.